The present invention relates to safety closures for pressure vessels and associated methods and systems. More particularly, in certain embodiments, the present invention relates to fluid loss cells that comprise safety closures.
Measurement of the filtration behavior and cake-building characteristics of drilling fluids may be useful to predict the effects of a particular drilling fluid on surfaces of a subterranean formation. Filtration characteristics of a drilling fluid may be affected by the quantity, type, and size of solid particles and properties of the liquid components of the fluid. Temperature and pressure may influence interaction of these various components. Therefore, filtration tests are often performed at both ambient temperature and at high-temperature conditions to provide data for comparison purposes.
High-pressure high-temperature (HPHT) fluid loss cells are standard pieces of equipment used for testing the performance of drilling fluids. These HPHT fluid loss cells may be used, for example, at temperatures of up to about 600° F. and pressures up to about 5000 psi. In general, HPHT fluid loss cells comprise a cylindrical body that defines a chamber for containing a pressurized test fluid and a circular pressure cap. A ceramic or paper filter may be housed inside the pressure cap. When the pressure cap is placed on the HPHT fluid loss cell, the cell may be pressurized and fluid present in the HPHT fluid loss cell may be displaced from the HPHT fluid loss cell through the filter. The pressure cap can then be removed to evaluate fluid loss properties of the fluid.
The use of conventional HPHT fluid loss cells may be problematic. Typically, conventional HPHT fluid loss cells may be opened while the cell is under pressure. For example, the pressure cap of the cell may be held in place by set screws, which can be removed while the cell is still under pressure. Opening these HPHT fluid loss cells while under pressure may potentially cause personal injury and property damage as the caps of the HPHT fluid loss cells may come off at a high rate of speed and force. Pressurization occasionally remains after venting due to the sample fluid plugging the pressurization port. To counteract this problem, pressure indicators have been placed on some cells and caps to indicate when the cell is pressurized. While this improves safety, the cell still may be opened under pressure. In addition, a special piece of hardware has also been designed to fit over the HPHT fluid loss cell to prevent explosive ejection of the cap, if the cell is opened under pressure. While this hardware may reduce the resultant explosive ejection, the hardware still allows opening of the cell while under pressure, requiring proper use of the cell to avoid injury.